1. Field of the Invention
The present invention relates generally to a method of and device for forming a vacuum sealed mold by assembling a pattern plate covered with a film with a molding flask, charging a heat-resisting particulate material into the flask, thereafter applying a shielding film over the upper surface of the flask, and reducing the pressure within the flask.
2. Description of the Prior Art
In the mold forming method of the type described, a sprue rod formed integral with a portion defining a pouring basin is made of a material such as foamed polystyrene, and is attached to a pattern or pattern plate covered with a film, so that a sprue and a pouring basin may be formed concurrently when a mold is formed. Alternatively, a conventional sprue rod wrapped with a film is attached to a pattern or pattern plate with an adhesive tape, and is removed after a mold is formed to form a sprue. Thereafter, an independent pouring basin is placed and communicated with the sprue. The former method is disadvantageous from the economical point of view because a sprue rod with a pouring basin forming pattern must be made of a material for each mold and when pouring molten metal, the sprue rod generates a lot of gas, so that it interfers the metal flow into the mold cavity. The latter method has also a disadvantage that the mold forming process becomes complicated because of the additional steps of wrapping film around a sprue rod, withdrawing the sprue rod upward, and placing a pouring basin.